The invention relates to a valve type of thermostatic device with a proportional-control actuator. The actuator includes a thermostatic element, such as a conventional expanding-wax thermostatic element, to give the device a back-up mode of operation if the actuator or its control gear should prove defective.
Thermostatic devices of the valve type are used, for example, in internal combustion engine cooling circuits for regulating the temperature of the cooling liquid (generally an aqueous mixture known as xe2x80x9ccoolantxe2x80x9d) introduced into the engine in order to optimize its operation. These devices act on a flow of xe2x80x9chotxe2x80x9d liquid coming from the vehicle engine and/or a flow of xe2x80x9ccoldxe2x80x9d liquid coming from a cooling radiator, and these flows are mixed to form a xe2x80x9cwarmxe2x80x9d cooling liquid which is reintroduced into the engine.
It should be noted that the words xe2x80x9chotxe2x80x9d, xe2x80x9ccoldxe2x80x9d and xe2x80x9cwarmxe2x80x9d are used with a view to simplifying the vocabulary to indicate relative temperature levels of the three streams of liquid when the device is operating in steady state. However, the respective temperatures of these three streams may be very similar, and may even be identical when the thermostatic device is still closed.
Thermostatic devices motorized by means of an electric motor comprising a back-up thermostatic element are already known. These devices may, for example make it possible, inside a chamber of the device, to mix a stream of cold liquid with the stream of hot liquid even when the engine or its control gear are defective, if the temperature of the liquid in which the thermostatic element is immersed exceeds a desired value. One particular example of this type of device is known from the French patent published under the number 2 703 730.
The thermostatic device in that document 2 703 730 is motorized by means of an electric motor comprising a rotary output shaft actuating the moving shutter of the thermostatic device by means of a conventional screw-nut coupling system that converts the rotary movement of the shaft into a translational movement. This moving shutter, such as a spool or xe2x80x9cplug,xe2x80x9d gradually uncovers a cold liquid inlet access of this device at the same time as it gradually shuts off a hot liquid inlet access, and vice versa. The back-up thermostatic element is aligned with the screw of the screw-nut system. When its temperature rises, its piston exerts a force on them plug, if the latter has not been moved or has not been moved far enough by the screw-nut system, and the force is oriented in the direction to uncover the cold liquid inlet access and to shut off the hot liquid inlet access so that under the thrust of the piston of the thermostatic element, the spool can actually move in that direction. The screw-nut system coupling is telescopic and, more specifically, mounted so that it can slide on the shaft of the motor, urged by a spring towards the plug in the direction to uncover the hot liquid inlet access and to shut the cold liquid inlet access. Thus, when the thermostatic element exerts a force on the plug in the opposite direction which is higher than that of the spring, in order to shut off the hot liquid inlet access and uncover the cold liquid inlet access, the spring is compressed by the retraction of the screw-nut system and there is then nothing to prevent this respective shutting-off and uncovering.
Because this device is of the plug valve type, it has a configuration which is sometimes difficult to tailor to certain engine and cooling circuit structures. Another disadvantage of this device is that when the temperature of the liquid in which the thermostatic element is immersed decreases, the screw-nut system accompanies the retracting movement of the thermostatic element which, because the electric motor or its control gear is defective, leads to a further rise in temperature, a further elongation of the thermostatic element, and an operation which tends towards instability with xe2x80x9cwarmxe2x80x9d liquid at a temperature appreciably higher than the desired temperature. In addition, the thermostatic element has to be relatively powerful in order to overcome the resistive force of the spring, and the screw-nut system with its telescopic spring-loaded mounting is relatively bulky, which means that the dimensions of the thermostatic device cannot be reduced as far as might be necessary.
It is an object of the invention to overcome these drawback. The invention therefore relates to a thermostatic device comprising a housing including fluid accesses so that it is possible for at least one fluid access to be shut off by a shutter. A metering actuator fixed to the housing and equipped with an output stem that can move in translation and is mechanically connected to the shutter in order to actuate this shutter in terms of translation selectively in a direction in which it gradually shuts off the access that can be shut off and in a direction in which it gradually, as a function of at least one engine operating parameter detected by at least one sensor, uncovers the access. A safety thermostatic element is situated at least partially in the stream of fluid and includes a part designed to actuate the shutter in translation when, as a result of defective operation, the latter has not been actuated by the metering actuator and the temperature of the stream of fluid exceeds, by a predetermined value, the temperature which should have given rise to such actuation by this actuator. The metering actuator is a proportional-control actuator consisting of an expanding-material thermostatic element also containing a heating means associated with the means for connecting the heating means to control gear involving a computer connected to the sensor, by which the metering actuator is driven through the connecting means.
By virtue of the fact that the proportional-control metering actuator is a thermostatic element designed to be heated at the command of a computer, rather than an electric motor such as a stepping motor, the cost price of the thermostatic device is appreciably lowered.
Conventional devices with two thermostatic elements have a metering thermostatic element, the expanding material of which is heated only by the fluid passing through the housing, and also have a thermostatic element for adjusting the threshold at which regulation began, and could be heated or not at the command of a computer. Thus a comparison between the conventional device and the present invention will clearly demonstrate that the device according to the present invention makes it possible to obtain a vehicle engine operating temperature which is always optimum from two points of view, including fuel consumption and pollutant emissions, irrespective of the load on this engine.
The thermostatic device may also exhibit one or more of the following features.
The heating means may comprise a resistive electrical component, and the connecting means may be electrical conductors designed to connect the resistive component to the control gear comprising the vehicle on-board computer.
The safety thermostatic element may be set to actuate the shutter in the opening direction at a fluid temperature a few degrees higher than the temperature at which the metering actuator is set to actuate the shutter in that direction.
The metering thermostatic element may be arranged in the housing downstream of the access that can be shut off by a shutter.
The metering thermostatic element may be carried by a support extending into a duct belonging to the housing.
The metering thermostatic element and the safety thermostatic element may be arranged one on each side of the access that can be shut off, and the metering thermostatic element may have an output stem which can move in terms of translation and which projects towards the shutter. The safety thermostatic element may have a piston, also projecting towards the shutter and facing the output stem, and the piston may be fixed to the output stem.
The safety thermostatic element may have a collar housed at least partially in skirt of the shutter.
The device may comprise a return spring resting against the shutter to exert a force on it that tends to return it in the direction of closing.
Finally, the output stem and the piston are secured together with the interposition of a thrust washer designed to be able to rest selectively, at the end of travel, against the free end of a ring of the metering element and against the free end of a ring of the back-up element.